Amplifying system



NOV. 17, 1931'. v, LANDON 1,832,640

AMPLIFYING SYSTEM Fi led May 27, 1929 nnnhu E INVENTOR Vernon D.Landon ATi'ORNEY 25 range of frequencies.

Patented Nov. 17, 1931 UNITED STATES PA-TENT OFFICE VERNON D. LANDON, OF WILKINSBURG, PENNSYLVANIA, ASSIGNOR TO WESTINGHOO'SE ELECTRIC & MANUFACTURING COMPANY, A CORPORATION OF PENNSYLVANIA AMPLIFYIN G SYSTEM Application filed May 27,

1 -5 It has been found hi hly desirable, in the construction of radiorequency'amplifiers, and particularly those of the type comprising means for, preventing self-oscillation, such as is shown and described in the Rice lo'Patent No. 1,334,118, to provide means whereby a predetermined amount ofregen- 'eration may be introduced for improving the sensitivity of the system. Such means preferably comprises a feed-back circuit associ- 18 ated with one of the thermionic tubes of the system that does not require neutralization against self-oscillation, the detector tube being, in general, chosen for this purpose.

In view of the present trend toward sim- 20 plification of radio receivers, it is desirable to adjust the sensitivity-control at the factory but, if this is done, it is found, byactual measurement, that satisfactory results cannot be. obtained over the entire broadcast If the feed-back circuit is adjusted for maximum sensitivity at the low-frequency end of the tuning range m of the receiver, the amount of feed-back is much too great at the higher end of the range and, as a consequence, the receiver is prone to oscillate when tuned to the higher frequencies. circuit is adjusted for the proper sensitivity at the higher frequencies, it'has only a slight effect in improving the sensitivity at the lower frequencies.

It is, accordingly, an object of my invention to provide an amplifying system, of the 40 regenerative type, wherein regeneration is limited, mainly, to those frequencies lying at thelower end of the tuning range.

Another object of my invention is to provide, in an amplifying system, means whereby the-sensitivity thereof is equally as good On the other hand, if the feed-back 1929. Serial No. 366,355.

at the low-frequency end of the tuning range as at the high-frequency end.

Another, and more specific, object of my invention is to provide an amplifying system, of the regenerative type, wherem re-- generation is automatically reduced at the high-frequency end of the tuning: range. In practicing my invention, include an lnductor, or radio-frequency choke coil, in

the plate circuit of a regenerative tube anda so proportion the constants of the inductor that it offers marked impedance to currents at the higher end of the tuning ran e of the amplifier. The said inductor, 'tierefore, tends to materially reduce regeneration at the higher frequencies while havingsubstantially. no effect upon regeneration at the lower end of the tuning range. V

I further provide a shunting condenser between the cathode of the tube and the end of the said inductor opposite to the end connected to the plate of the tube, and tune the series circuit so constituted to a frequency lying at the upper end of the tuning range of the amplifier. The said series-tuned circuit, hereinafter designated the high-frequency sensitivity control circuit, therefore, offers low impedance to the higher frequencies impressed on the tube and, consequently, by-passes currents at such frequencies away from the feed-back coil provided for regeneration. r W 3 The novel features that I consider characteristic of my invention are'set forth with particularity in the appended claims. The invention itself, however, both'as to, its organization and its method of operation, to-

gether with additional 'objects'and advantages thereof, will best be understood from the following description of a specific embodiment, when readin connection with the accompanying drawing.

The single figure of the drawing is a diagrammatic view of a p'ortion of an amplifying system comprising a preferred embodiment of my invention.

The apparatus illustrated in the drawing comprises a radio-frequency amplifier tube 1 and a detector tube 2. The amplifier tube is provided with an input circuit constituted by a tuning condenser 3 and an inductor l. The output circuit of the amplifier tube is constituted by an inductor 5, preferably, though not necessarily, having a natural period below the tuning range of the input circuit. A condenser 8 is interposed between the plate of the tube 1 and the lower end of the input inductor 4, as disclosed in the aforementioned Rice patent. If the output circuit constituted by the inductor 5 is inductive over the tuning range, the condenser 8 neutralizes the tendency of the amplifier toward oscillation; if the output inductor offers a capacitive reactance over the tuning range, the condenser 8 provides positive feed back, as disclosed in the co-pending application of George L. Beers, Serial No. 151,722, filed November 18, 1926, and assigned to the \Vestinghouse Electric & Manufacturing Company.

The output inductor 5 of the amplifier tube is coupled to an inductor .6 around which is shunted a tuning condenser 7, the inductor and condenser constituting the input circuit for the detector tube.

The detector tube is provided with a feedback circuit comprising an inductor 9 and a variable condenser 10, the said circuit being connected between the plate and the filament of the detector tube, and the inductor being coupled to the output inductor 5 of the amplifier tube, as well as to the input inductor 6 of the detector tube.

Plate potential for the amplifier tube and the detector tube is supplied from a common source 11, the direct-current supply circuit for the detector tube including the primary winding 12 of an audio-frequency transformer 13. The secondary winding 14 of the transformer may be connected to succeeding stages of audio-frequency amplification (not shown). A common source 15 supplies filament potential for both tubes.

An inductor 16, preferably of resistance wire to minimize parasitic oscillations, is interposed between the plate of the detector tube and the terminal of the primary winding of the audio-frequency transformer which is connected thereto, and one terminal of an adjustable condenser 17 is connected to the end of the inductor opposite the end which is connected to the said plate. The other terminal of the adjustable condenser is connected to a grounded conductor 18 that is common to the filament circuits of both tubes.

During the construction of an amplifving system, according to my invention, the feedback condenser 10 is so adjusted as to give satisfactory sensitivity at the lower end of the tuning range. The series-tuned circuit, constituted by the inductor 16 and the condenser 17, is next so tuned as to be resonant to a frequency at or near the highest frequency the system is designed to amplify. This frequency is in the neighborhood of 1500 kilocycles if the system is to be utilized for the reception of broadcast programs.

Condenser 8 may be adjusted to give the desired sensitivity at high frequencies, and condenser 10 may be used to adjust the sensitivity at low frequencies. Thus, the sensitivity curve may be made flat or may be made to favor either end of the scale desired.

By introducing the series-tuned circuit, constituted by the inductor 16 and the adjustable condenser 17 between the plate and filament of the detector tube, and by tuning this circuit to a frequency at or near the highest frequency to which the input circuit of the detector tube is tunable, an effective by-pass will be provided for the higher frequencies and will materially reduce regeneration thercat.

In one successful commercial embodiment of my invention, the constants thereof are as follows:

Inductor 16, from 11 to 14 turns of No. 36 resistance wire on a tube f in diameter.

Inductor 5, 450 turn universal-wound coil.

Inductor 6, 100 turns ,No. 28 wire on a tube 11%; in diameter and spaced 31;" from inductor 5.

Inductor 9, 20 turns No. 28 wire on a tube 1,- in diameter.

Condenser 17, approximately 800 mmf.

Condenser 10, approximately mmf.

It will, accordingly, be apparent that I have, by my invention, provided a very important improvement, in amplifying systems of the regenerative type, by which maximum sensitivity may be secured over the entire tuning range without introducing any tendency toward self-oscillation at the higher frequencies thereof.

Although I have chosen a specific embodiment of my invention for purposes of illustration, the invention is not restricted to the exact circuitdescribed, inasmuch as manyv transferring energy from said output circuit to said input circuit to secure regeneration and means, including a series-tuned circuit, for lessening said energy transfer at high frequencies. said series tuned circuit offering minimum impedance to frequencies at" the high frequency end of the broadcast range.

2. In an amplifying system, a thermionic device, an input circuit for said device, an output circuit for said device, means for transferring energy from said output circuit to said input circuit to secure regeneration, and means including aseries-tuned circuit in parallel to said regeneration means, said series-tuned circuit ofi'ering minimum impedance to frequencies at the higher frequency end of the broadcast range.

In testimony whereof, I have hereunto subscribed my name this 23rd day of May, 1929. VERNON D. LANDON. 

